Active Fault and Paleoearthquake Researches No. 9 (2009)

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A trench wall showing evidence for the penultimate surface rupturing earthquake on the fault caused the 2008 Iwate-Miyagi Nairiku earthquake at Okayama, Ichinoseki City, Iwate Prefecture, Japan

The 2008 Mw 6.9 Iwate-Miyagi Nairiku earthquake was accompanied by 20 km-long surface rupture. We excavated a trench across the 2-3-m-high pre-existing fault scarp on a river terrace at Okayama district where 10-cm throw and 20-cm shortening of an asphalt paved road was observed immediately after the earthquake. Significantly deformed terrace gravel and overlying loam units due to thrust faulting were exposed in the trench (see detail in Maruyama et al on pages 19-54).

Shinji Toda and Tadashi Maruyama